title: High-resolution structure of a papaya plant-defense barwin-like protein solved by in-house sulfur-SAD phasing.
abstract: The first crystal structure of a barwin-like protein, named carwin, has been determined at high resolution by single-wavelength anomalous diffraction (SAD) phasing using the six intrinsic S atoms present in the protein. The barwin-like protein was purified from Carica papaya latex and crystallized in the orthorhombic space group P212121. Using in-house Cu Kα X-ray radiation, 16 cumulative diffraction data sets were acquired to increase the signal-to-noise level and thereby the anomalous scattering signal. A sequence-database search on the papaya genome identified two carwin isoforms of 122 residues in length, both containing six S atoms that yield an estimated Bijvoet ratio of 0.93% at 1.54 Å wavelength. A systematic analysis of data quality and redundancy was performed to assess the capacity to locate the S atoms and to phase the data. It was observed that the crystal decay was low during data collection and that successful S-SAD phasing could be obtained with a relatively low data multiplicity of about 7. Using a synchrotron source, high-resolution data (1 Å) were collected from two different crystal forms of the papaya latex carwin. The refined structures showed a central β-barrel of six strands surrounded by several α-helices and loops. The β-barrel of carwin appears to be a common structural module that is shared within several other unrelated proteins. Finally, the possible biological function of the protein is discussed.
authors.affiliation: Laboratoire des Biopolymères et des Nanomatériaux Supramoléculaires (CP206/04), Faculté de Pharmacie, Université Libre de Bruxelles, B-1050 Brussels, Belgium.
authors.forename: Joëlle
authors.initials: J
authors.lastname: Huet
authors.forename: Emmanuel Jean
authors.initials: EJ
authors.lastname: Teinkela Mbosso
authors.forename: Sameh
authors.initials: S
authors.lastname: Soror
authors.forename: Franck
authors.initials: F
authors.lastname: Meyer
authors.forename: Yvan
authors.initials: Y
authors.lastname: Looze
authors.forename: René
authors.initials: R
authors.lastname: Wintjens
authors.forename: Alexandre
authors.initials: A
authors.lastname: Wohlkönig
mesh_terms: D000595:Amino Acid Sequence; D029441:Carica / Q000737:chemistry* / Q000235:genetics; D003460:Crystallization / Q000379:methods; D018360:Crystallography, X-Ray; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation; D016415:Sequence Alignment; D013455:Sulfur / Q000737:chemistry*; D014961:X-Ray Diffraction / Q000379:methods*; D017307:Xamoterol / Q000737:chemistry
chemical_list: D010940:Plant Proteins; C076873:barwin protein, Hordeum vulgare; D013455:Sulfur; D017307:Xamoterol
keywords: Carica papaya; barwin-like protein; carwin; sulfur-SAD phasing